In present telecommunications technology the asynchronous transfer mode (ATM) based on asynchronous time-division multiplex technology plays a critical part in the development of integrated services broadband networks (B-ISDN). In this mode the signal transmission proceeds in a bit: stream that is subdivided into cells of a constant length of, for example, 53 octets, each of which is respectively composed of header and useful information part and that are occupied as needed with packeted messages. When no useful information is to be communicated, then specific empty cells are transmitted. Virtual connections, that is, connections that only use a path section when a message packet (block) is in fact to be transmitted thereover, are set up in ATM switching centers. Each packet contains, among other things, an address covering, for example, two octets in its header for the unambiguous allocation of the packet to a specific virtual connection. Based on the criterion of the respective selection information, every packet at the input to the switching network can thereby receive the complete information for its route through the switching network. The switching elements then automatically through-connect the packet on the defined route using this information (self-routing network, see, for example, Telcom Report 11 (1988) 6, 210 . . . 213). A two-stage reversing switching network having (2n.times.2n) ATM switching modules can thereby be provided as a switching network. These switching modules can in turn be respectively formed with a plurality of switching elements for switching (routing and queuing) ATM cells from 2.multidot.n simplex inputs via a preferably central ATM cell memory to n simplex outputs (IEEE Journal on Selected Areas in Communications, vol. 9, no. 8, October 1991, 1299 . . . 1307, FIGS. 3, 5, 7, 8). An ATM multiplexer/demultiplexer (that is, a multiplexer or a (de)multiplexer, as appropriate) can also be inserted between subscriber lines of the subscriber side and the ATM switching network. This multiplexer/demultiplexer can also be formed with a plurality of switching elements for switching (routing and queuing) ATM cells from 2.multidot.n simplex inputs via a preferably central ATM cell memory to n simplex outputs (IEEE Journal on Selected Areas in Communications, a.a.O., p. 1301 and FIG. 2).
It has already been disclosed (see U.S. Pat. No. 5,291,478) for such an ATM switching system to also through-connect short routes in the first stage of the ATM switching network via which the input lines are connected to output lines of the ATM switching network without making use of the second stage of the ATM switching network.
In an ATM switching system wherein an ATM multiplexer/demultiplexer also lies between subscriber lines of the subscriber side and the ATM switching network, the demand for short routes can also occur in such a multiplexer/demultiplexer. The present invention discloses a way to accomplish this.